The proposed research will evaluate the role of oculomotor adaptation in the development and progression of myopia. Although there is little doubt of an environmental influence on myopia, the identity of precursors and quantitative methods for study remain elusive. Recently, it was shown that short periods of near-work may induce adaptive changes in the rest focus and rest convergence of the eyes. Thus it appears reasonable that a normal visual environment can result in habitual accommodative and/or convergence adaptation. Habitual adaptation will cause sustained contraction of the ciliary muscle and the extraocular muscles of convergence whenever the accommodative and convergence feedback-loops are opened (for example, when the eyes are closed in sleep). The long-term effect of this process may be to produce sufficient stress on the globe to induce myopic elongation. These effects also may cause structural modification of the extraocular muscles, or their attachments, leading to permanent change in the ocular deviation (phoria position) of the eyes. The proposed research will test the hypothesis that habitual adaptation is a precursor of myopia and binocular imbalance. A new technique is derived in this proposal to calculate accommodative and convergence adaptation from measurements of open-loop and partial open-loop accommodation and convergence responses. The specific aims are: (1) to measure the contribution of habitual adaptation to rest focus and rest convergence (2) to determine the effect of adaptation on the origin of the phoria position (3) to establish if there are differences in the propensity for adaptation between myopes and emmetropes (4) to evaluate the effect of optical and prismatic corrections on adaptation in myopia and (5) to define the association of habitual adaptation to the rate of myopic progression. The long-term goal of this research is to establish a new methodology to promote continued study of the etiology of myopia and ocular deviation.